In oil and gas wells there are now an increasing tendency to install downhole equipment for control and monitoring of a production flow and/or well conditions, in particular in order to provide better information on the downhole conditions in well systems of increasing complexity. Some downhole equipment is installed for being used over a longer period of time and requires permanent connections into the well. Such connections are required for the transfer of necessary electrical, optical and/or hydraulic signals to the downhole equipment. For electrical and optical signals the connection is typically designed as a relatively thin instrument tube using corrosion resistant metal which protects the electrical and/or optical connections arranged inside the instrument tube, cemented in a filler material. When transmitting hydraulic signals the same type of instrument pipe is used, however without any filler in order that the void can be used to transfer pressure via hydraulic fluid which fills the instrument tube.
Many oil- and gas wells are operating under such a high pressure that breakage or leakage in the part of the instrument tube which is inside the well may occur, resulting in pressure propagating through the instrument pipe, even if the instrument pipe is filled with conductors and filler material. In gas wells, in particular, the pressure will propagate inside the instrument pipe all the way up to the surface. For this reason it is normal to specify the use of a dedicated pressure barrier for the possibility of well pressure inside the instrument tube. Such a barrier will be placed at the end/termination of an instrument tube/pipe, typically as part of a well head barrier assembly.
A well head barrier can be used as signal connector for routing electrical/optical/-hydraulic signal through a well head. Downhole devices, such as downhole mounted sensors, are typically connected to cables running from a downhole location, and inside the well tube to a cable terminating location at the end of the well tube, in a so-called well head.
A pressure barrier for a hydraulic signal typically consists of a valve which manually or automatically closes the well pressure upon a possible breakage of the instrument tube inside the well. A pressure barrier for an electrical or optical signal may be a so-called penetrator and consists of one or more signal conductors which are made pressure tight. This can be done by sealing or encapsulating the optical or electrical conductors in a pressure tight filler material.
By arranging such a pressure barrier for the instrument tube at the well head two barriers are achieved, one consisting of the instrument tube itself and one in the pressure barrier. As known for a person skilled in the art, there are problems and challenges regarding leaks at full well pressure in an instrument tube. However, the well head barrier assembly according to the present invention removes this risk, which increases the safety of the well regarding for instance explosion or fire risk. At a possible breakage of the instrument tube inside the well, a leakage will be stopped before a leakage to the outer environment has occurred.
The disadvantage of a breakage of the instrument pipe is that after the breakage there will be full well pressure at the well head and there is a single pressure barrier separating the well pressure from the environment. If a breakage has occurred in a production pipe in an oil and gas well, the pressure can be controlled by pumping high density drilling fluid into the well. However, present solutions for optical/electrical/hydraulic pressure barriers for downhole equipment does not include a possibility for balancing the pressure inside the instrument tube.